Which condition describes an isochoric process?

An isochoric process is characterized by a constant volume. In this type of thermodynamic process, the system does not exchange any work with its surroundings in terms of volume change since the volume is held constant throughout the process. This means that as a substance undergoes heating or cooling in an isochoric process, any heat exchanged will result in a change in temperature or internal energy, but the physical volume of the system does not change.

In this context, the distinction between different thermodynamic processes is crucial. Constant pressure refers to an isobaric process, while constant temperature indicates an isothermal process. Constant internal energy is more specific to certain conditions that may or may not apply to an isochoric process, as the internal energy of a system can change with temperature variations even if the volume remains constant. Therefore, the defining characteristic of an isochoric process is indeed that the volume does not change, making it the correct answer.